Current data suggest that SARS-CoV-2 reinfections are rare. Uncertainties remain, however, on the duration of the natural immunity, its protection against Omicron variant, and on the impact of vaccination to reduce reinfection rates. In this retrospective cohort analysis of the entire population of an Italian region, we followed 1,293,941 subjects from the beginning of the pandemic to the current scenario of Omicron predominance (up to mid-February 2022). After an average of 277 days, we recorded 729 reinfections among 119,266 previously infected subjects (overall rate: 6.1‰), eight COVID-19-related hospitalizations (7/100,000), and two deaths. Importantly, the incidence of reinfection did not vary substantially over time: after 18–22 months from the primary infection, the reinfection rate was still 6.7‰, suggesting that protection conferred by natural immunity may last beyond 12 months. The risk of reinfection was significantly higher among females, unvaccinated subjects, and during the Omicron wave.
This retrospective cohort study compared the rates of virologically-confirmed SARS-CoV-2 infections, symptomatic or lethal COVID-19 among the residents of the Italian province of Pescara who received one or two doses of COVID-19 vaccines, versus the unvaccinated. The official data of the National Health System were used, and a total of 69,539 vaccinated adults were compared with 175,687 unvaccinated. Among the subjects who received at least one vaccine dose, 85 infections (0.12%), 18 severe and 3 lethal COVID-19 cases were recorded after an average follow-up of 38 days. Among the unvaccinated, the numbers were 6948 (4.00%), 933 (0.53%) and 241 (0.14%), respectively. The serious adverse event reports—yet unconfirmed—were 24 out of 102,394 administered doses. In a Cox model, adjusting for age, gender, and selected comorbidities, the effectiveness of either BNT162b2, ChAdOx1 nCoV-19 or mRNA-1273 vaccines was higher than 95% in preventing infections (mostly due to B.1.1.7 variant), symptomatic or lethal COVID-19. No differences were observed across genders, and among the 691 subjects who received the second dose of vaccine later than the recommended date. Although preliminary, these findings support current immunization policies and may help reducing vaccine hesitancy.
We performed a cohort analysis of the entire population of Abruzzo, Italy, to evaluate the real-world effectiveness of SARS-CoV-2 vaccines against infection, COVID-19 hospitalization or death, over time and during the Omicron wave. All resident or domiciled subjects were included, and official vaccination, COVID-19, demographic, hospital and co-pay exemption datasets were extracted up to 18 February 2022. Multivariable analyses were adjusted for age, gender, hypertension, diabetes, major cardio- and cerebrovascular events, COPD, kidney diseases, and cancer. During the follow-up (average 244 days), 252,365 subjects received three vaccine doses (of BNT162b2, ChAdOx1 nCoV-19, mRNA-1273 or JNJ-78436735), 684,860 two doses, 29,401 one dose, and 313,068 no dose. Overall, 13.4% of the individuals were infected with SARS-CoV-2 (n = 170,761); 1.1% of them had severe COVID-19, and 0.6% died. Compared with the unvaccinated, those receiving two or three vaccine doses showed an 80% to 90% lower risk of COVID-19 hospitalization or death. Protection decreased during the Omicron wave and six months after the last dose, but it remained substantial. Lethal disease was uncommon during the Omicron wave and in the young population, even among the unvaccinated. Some of the current policies may need a re-evaluation in light of these findings. The results from the Omicron wave will inevitably require confirmation.
Background Current data suggest that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfections are rare, but no information are available on minors and after 12 months of follow-up. Methods This retrospective cohort study included all the population of an Italian Province, diagnosed with a SARS-CoV-2 infection from March 2020 to May 2021. The primary outcome was the incidence of a reinfection, defined as a new positive polymerase chain reaction (PCR) test occurring ≥90 days after complete resolution of the first infection, and data were retrieved from the official datasets (coronavirus disease 2019 [COVID-19], demographic, hospital and co-pay exemption) of the Local Health Unit (LHU) of Pescara. Results After an average of 201 days of follow-up (max. 414), we recorded 24 reinfections ≥90 days after the resolution of the first 7173 infections (0.33%). Four reinfections required hospitalization, one was lethal. Most of the reinfections (n = 13) occurred 6–9 months after the resolution of the first infection; no new infection was detected 12 or more months later and among the 832 minors. Conclusions This study confirms previous findings on a low risk of SARS-CoV-2 reinfection. If confirmed, these findings suggest that more targeted restriction policies can be applied to the subjects that recovered after a first infection.
Current data suggest that SARS-CoV-2 reinfections are rare, but uncertainties remain on the duration of the natural immunity, its protection against Omicron variant, finally the impact of vaccination to reduce reinfection rates. In this retrospective cohort analysis of the entire population of an Italian Region, we followed 1,293,941 subjects from the beginning of the pandemic to the current scenario of Omicron predominance (up to mid-January 2022). After an average of 334 days, we recorded 260 reinfections among 84,907 previously infected subjects (overall rate: 0.31%), two hospitalizations (2.4 x100,000), and one death. Importantly, the incidence of reinfection did not vary substantially over time: after 18-22 months from the primary infection, the reinfection rate was still 0.32%, suggesting that protection conferred by natural immunity may last beyond 12 months. The risk of reinfection was significantly higher among the unvaccinated subjects, and during the Omicron wave.
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